By 'know', he means 'be in the same region'.
The elder priest doesn't do anything himself. It's the character inviting the elder-priest in the same region to give a sermon. I believe Actions for that link is correct though. It says 'Invite a Priest...' I believe.
EDIT: After the invitation, *then* the elder priest does write something up as a reply. Then, the other character can accept to join the religion. And provide the priest a donation of gold.